Well, that would make sense, considering our non-Aboriginal heritage is mostly Brits, and a fair few of those are convicts, however many were sent here for crimes as small as shovel theft. Not to mention the whole "everything trying to kill us" thing.
Kinda sounds like a British person wrote it, though. I've never actually heard the expression "on side" in the US. The US expression is usually "on my side," "beside me," or "at my back."
To be fair, I only interact regularly with three British people; it's just that the only place I've ever heard the phrase "on side" used is BBC programming like Midsomer Murders.
On the one hand, considering this is a quote, it could've simply been a poor transcript or a typo. On the other hand, Spetsnaz were created post-WW2, so it is highly unlikely any American soldier would've ever fought alongside Spetsnaz. At best they would've called them something else like Commandos or Marine Raiders.
But yeah, it may still have been forged :)